There is known a method for generating a swirl in cylinders of an internal combustion engine in an air supply process to improve combustibility.
PTL 1 described below discloses a configuration including an intake port that functions as a swirl generation port for generating a swirl which turns along an inner peripheral surface of each of cylinders. In the invention described in the above literature, an opening position of the intake port that is the swirl generation port provided in a cylinder on a first end side of a cylinder head, and an opening position of the intake port that is the swirl generation port provided in a cylinder on a second end side are deviated from each other in the opposite directions from the centers of the cylinders, so that the turn directions of respective swirls generated in the cylinders are opposite from each other. Consequently, even when a core for an intake port is contracted during manufacture, the directions in which the respective opening positions of the intake ports are deviated become the same, and variation in swirl ratios of the cylinders can be suppressed.
Additionally, as described in the following PTL 2, there is known an internal combustion engine in which swirl chambers are provided in respective ends of a plurality of cylinders. In FIG. 7 and FIG. 8, diagrams disclosed in the above literature are illustrated. FIG. 7 illustrates a periphery of an air supply manifold 101 of the multiple cylinder internal combustion engine having a plurality of cylinders 100. In FIG. 7, only one cylinder 100 among the plurality of cylinders is illustrated as a representative cylinder. To the air supply manifold 101, one air supply introduction pipe 103 that supplies air into the air supply manifold 101 is connected. A downstream end of the air supply introduction pipe 103, that is, a connecting part with the air supply manifold 101 serves as an air supply inlet 103a to the air supply manifold 101. Between the air supply manifold 101 and respective cylinders 100, air supply ports 105 are provided. These air supply ports 105 guide supplied air to the respective cylinders 100. Between the respective air supply ports 105 and the cylinders 100, swirl chambers 107 are provided. Each of the swirl chambers 107 forms a swirl to supplied air which is guided from the respective air supply ports 105. More specifically, as illustrated in FIG. 8, a swirl chamber inlet 107a is provided at a position eccentric from a central axis CL of each of the swirl chambers 107, and supplied air which flows into from this swirl chamber inlet 107a turns around the central axis CL. As illustrated in FIG. 8, when an air supply valve 109 is opened, supplied air obtained after a swirl is formed in each swirl chamber 107 flows into the cylinder 100, and a desired swirl ratio is obtained in the cylinder 100. The arrow A of FIG. 7 illustrates the swirl direction inside the cylinder 100.
In PTL 2, there is a solution for a problem that distances between the air supply inlet (main flow generation starting point) 103a for supplying air to the air supply manifold 101 and the air supply ports 105 are different for the respective air supply ports 105, and therefore flow distributions are different, and variation in respective swirl ratios formed in the swirl chambers 107 occurs. In order to solve this problem, in accordance with relative distances of air supply ports 105 relative to the air supply inlet 103a, the central axes of the air supply ports 105 are eccentric to the central axes CL of the swirl chambers 107, so that the flow distributions of supplied air are adjusted, variation in the respective swirl ratios of the swirl chambers 107 is suppressed, and supplied air flows in the respective cylinders 100 are made to be equal.